1. Field of the Invention
The present invention relates to the field of optical viewing systems, and in particular, to optical viewing systems that simultaneously display images from at least two video sources.
2. Prior Art
Humans have binocular vision for perceiving three dimensional scenes, that is, scenes having depth as well as height and width. A single viewing apparatus such as a single human eye, can perceive scenes only two dimensionally. The perception of depth in a three dimensional space is due to the difference in the angle or relative position of features of the scene at different distances from the viewer, in views taken from two spaced points of view, also known as parallax.
It is known to simulate a three dimensional image using dual two dimensional media. Two images of the same scene are prepared, each being a two-dimensional view of the three dimensional scene, but the two being taken from laterally spaced positions. When viewing one image with one eye and the other image with the other eye, the viewer perceives the image to have depth, in the same manner that the user's eyes perceive depth in actual three dimensional scenes.
An individual can view such a specially processed or configured dual two dimensional image through special eyeglasses. For example, the dual images can be superimposed on one two-dimensional viewing area and separated using light polarization. One of the dual two-dimensional images is presented in light polarized at one angle, and the other is presented in light polarized 90 out of phase with the first. The observer views the superimposed images through eyeglasses which have lenses polarized in a complementary manner to separate the dual images such that one is presented to each eye. Each lens transmits one form of polarized light and inhibits passage of the other form of polarized light. The eyes of the viewer essentially receive images of the three dimensional scene from different perspectives, and the brain interprets the dual two dimensional images as one scene having depth.
Various optical systems for producing three dimensional images in this manner are known, such as systems using lenticular lenses and films, and other stereoscopic systems which include lenses or prisms for transmitting the two images separately, one to each eye.
Normally, stereoscopic scenes are static. However, moving pictures can also be accomplished. The two images can be projected from a single two dimensional projection, and separated by use of complementary colors, polarization or distinct diffracted light paths. In U.S. Pat. No. 4,740,836--Craig, dual two dimensional images taken from slightly different perspectives are displayed side by side on one CRT, and are recombined for viewing using prisms which diffract the light from the lateral sides of the CRT so that each eye views one side of the CRT only. In U.S. Pat. No. 4,647,966--Phillips at al, two images at distinct polarization angles are projected on one view screen and are viewed through polarized glasses. See also, for example, U.S. Pat. No. 4,573,759; 4,487,490; 4,552,443; and 3,695,878.
A somewhat different form of three dimensional image can be provided by producing two or more two-dimensional images or image layers which are projected to appear at different distances from the observer, and are viewed through one another with both eyes. Each layer shows only those elements of the three dimensional scene which are at equal distance from the viewer of the scene, each image layer then being projected such that the features in the nearer levels appear to be placed closer to the observer and in front of the features of one or more layers in a more remote level.
In a simplest form, a two dimensional image showing only items in a foreground scene (being otherwise transparent) is presented in front of a two dimensional image of a background scene, the apparent spacing of the foreground and the background layers providing the image with depth. More complex forms can have a plurality of layers. The latter, layered form of display has a number of implications for projection and viewing. In a layered projection the observer's binocular vision is used directly to provide the perception of depth, unlike stereoscopic systems wherein the perception of depth is provided by presenting different views to the respective eyes. It is the lateral spacing of the observer's eyes that provides the difference in views, or parallax. A layered three dimensional scene is not the same from all angles relative to the viewing screen as it is in a separated perspective or stereoscopic image system wherein the separation of the cameras or the like which recorded the scene defines the parallax. Viewing a layered three dimensional scene can be more comfortable for the observer than viewing stereoscopic images, which may require substantial concentration.
Layered two dimensional images are geometrically less complicated than stereoscopic images because less attention is required with respect to angles. However layered images involve the further step of separating the foreground features (for presentation in a transparent field) from the background features (viewed through the transparent field). Layered images also require a substantially different projection apparatus than stereoscopic images, for projecting the layers at different apparent distances from the observer. Nevertheless, layered two dimensional images are appropriate and useful, especially due to the lack of angular complexity in the recording phase.
In U.S. Pat. No. 4,190,856--Ricks, a three dimensional television apparatus based on superimposed two dimensional layers is disclosed. However the apparatus is complex, and notwithstanding the complexity there are certain problems that are encountered, for example with respect to opacity of the foreground features and the size of the projection apparatus. The projection of individual layers is achieved using plural projection CRTs. CRTs inherently define a substantial length along the center axis or Z axis of the electron beam, and also occupy a relatively large space laterally of the Z axis, for the deflection yoke. The individual CRTs according to Ricks are disposed at lateral spaces and along orthogonal axes in order to provide space for the CRTs. The image from each CRT is transmitted along a respective path, the paths traversing full and/or half silvered mirrors whereby the images are combined to appear at different perspectives. According to one embodiment the foreground images are reduced in size for recombination, requiring lenses, and resulting in a composite image wherein the image from a foreground layer is overlaid on only a part of a larger background layer. For a four layer arrangement, even using images of equal size, the arrangement is quite complex.
Another problem relates to simultaneously displaying images from different video sources which may not be related to one another, in the sense of creating a three dimensional image. It is often desirable to view video images from disparate video sources at the same time, for example by enabling a first display to be continuously monitored, while at the same time accessing one or more other displays to monitor other events or information. At present, such displays are usually implemented by picture-in-picture displays or split screens, each of which result in some image material being blocked by an overlaid picture image.
It would be desirable to provide an optical viewing system which can be adapted not only for three dimensional simulation, but for simultaneously displaying images from plural video sources which are not related in the sense of being needed to create a three dimensional simulation, and which at the same time is compact, easy to operate and easy to view.